As with most other fashion rules - no white after Labor Day, always wear hose with dresses and skirts, no shorts after summer - the rule against wearing black with brown has been thrown out the window. The pairing of black and brown can create a very rich look. The trick is to choose a brown that has some depth. Flat, matte true browns without depth cannot create a contrast against black, causing the colors to clash. Browns with depth, meaning those that feature an undertone color, create the illusion of depth and contrast with black, allowing the colors to work in concert. There are no particular undertones that must be paired with black, though I find medium-to-deep browns with warm undertones work best as they provide the most contrast. Should you wear a couple of brown items with black, there is no need to match the browns. The more depth, the better. Rather than getting hung up on specific shades, though, it's more important to focus on the visual depth you're creating. If the outfit has depth, you're on your way. If the brown and black you're wearing seem to clash, you probably need to find a more complex brown.